1. Field of the Invention
This invention relates to an engine control system for a hybrid vehicle, and, more particularly, to an engine control system which stops or restarts the engine in consideration of the remaining charge of a high-voltage battery and the amount of power consumption by accessories or other devices.
This application is based on Japanese Patent Application No. 11-62414, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles which carry motors as power sources for driving the vehicles in addition to engines are known. Hybrid vehicles are divided into series hybrid vehicles and parallel hybrid vehicles. In the series hybrid vehicles, the engine drives a generator whose electric power output is used to drive the motor, which in turn drives the wheels. In the parallel hybrid vehicles, the motor coupled to the engine assists the rotation of the drive shaft of the engine while charging a high-voltage battery with electric energy using the motor itself as a generator or using a separate generator.
Because the engines of such hybrid vehicles can constantly run within the engine-speed range of a high fuel mileage and a low emissions level or their drive loads can be reduced, the hybrid vehicles can achieve lower fuel consumption and lower emissions levels than conventional engine vehicles.
As disclosed in, for example, Japanese Unexamined Patent Application, First Publication Hei 8-317505, some of those hybrid vehicles are designed to be capable of stopping the operation of the engine in accordance with predetermined driving conditions.
Because of the ability to stop the operation of the engine, such a hybrid vehicle is superb in preventing over-charging of the battery or achieving a further improvement on the fuel consumption by stopping the operation of the engine in accordance with predetermined operational conditions, such as the remaining charge of the battery, but has the following problem.
For example, while a certain amount of energy remains in the battery when fuel supply cut is carried out during deceleration, it is not adequate to keep fuel supply cut and stop the engine when the 12-V system consumes a large amount of power and energy should be supplemented from the high voltage battery to the 12-V battery, e.g., when turning on head lights while driving the vehicle in a night.